Process and apparatus for visualizing gamma ray images

ABSTRACT

A process and a device for visualizing gamma ray images use a semi-conducting plate which is provided on both sides with electrode strips extending parallel to each other, the direction of the strips on one side extending at an angle to the direction of strips on the other side. The invention is particularly characterized in that the gamma quanta are changed into electron bundles and are represented upon the semi-conducting plate. The electrode strips are connected with a device for core formation which produces representable local signals localizing the electron bundle striking the semi-conducting plate.

United States Patent 1191 Prag et a1.

[ PROCESS AND APPARATUS FOR VISUALIZING GAMMA RAY IMAGES [75] Inventors:Rudolf Prag, Marloffstein; Joachim Dierker, Buckenhof, both of Germany[73] Assignee: Siemens Aktiengesellschaft,

Erlangen, Germany 221 Filed: Nov. 3, 1971 211 Appl. No: 195,345

[52] U.S. Cl. 250/370, 250/366 [51] Int. Cl. G01! 1/24 [58] Field ofSearch... 250/715 R, 83.3 R, 213 VT,

9/1970 Oosthoek et a1. 250/833 R 1 51 May21, 1974 3,683,185 8/1972Muehllehner 250/7l.5 R

Primary ExaminerArchie R. Borchelt Assistant Examiner-Davis L. WillisAttorney, Agent, or Firm-Richards & Geier [57] ABSTRACT A process and adevice for visualizing gamma ray images use a semi-conducting platewhich is provided on both sides with electrode strips extending parallelto each other, the direction of the strips on one side extending at anangle to the direction of strips on the other side. The invention isparticularly characterized in that the gamma quanta are changed intoelectron bundles and are represented upon the semiconducting plate. Theelectrode strips are connected with a device for core formation whichproduces representable local signals localizing the electron bundlestriking the semi-conducting plate.

5 Claims, 3 Drawing Figures HTENTEUVAY 21 I974 sum 1 or z INVEIYTORS.

ATTOYLNCSS PROCESS AND APPARATUS FOR VISUALIZING GAMMA RAY IMAGES Thisinvention relates to a process and a device for visualizing gamma rayimages by means of a semiconducting plate which makes possible todetermine the location of absorption of an ionizing particle, in that itis provided on both sides with electrode strips extending parallel toeach other, whereby the direction of the strips upon one side forms anangle with the direction of strips upon the other side. A device of thistype is used, for example, in the nuclear medical diagnosis to makevisible the distribution of incorporated radioactive substances whichare preferably fed to certain organs or sick tissues.

Semi-conducting devices, particularly in the shape of semi-conductingplates, which make possible a localization of the absorption place ofionized ray emission, are known in the art. These devices consist, forexample, of a semi-conducting plate the opposed principal surfaces ofwhich are provided with parallel electrode strips, whereby the directionof strips upon one side forms an angle with the strips upon the otherside, preferably an angle of 90. The contacts between the electrodes andthe semi-conducting, plate have upon one side a rectifying and upon theother side an ohmic characteristic.

These known semi-conducting detectors have not found acceptance up tonow since due to the small produceable layer strengths they have only asmall absorpton probability and thus a small output for the gamma rays.Furthermore, they can not be made of sufficiently large surface sizes,to be able to be used directly for representing the distribution ofradioactive substances in an organism.

An object of the present invention is to eliminate these drawbacks ofexisting constructions.

Other objects will become apparent in the course of the followingspecification.

In the accomplishment of the objectives of the present invention it wasfound desirable to transform the gamma ray image into an electron rayimage which is then represented upon the semi-conducting plate, theelectrode strips of which are connected with a device for core formationand for producing representable local signals for localizing theelectron bundle striking the semi-conducting plate.

The transformation into the electron image can be carried out with asuitable device, for example, a scintillator-photo-cathode combination,such as is used for image changers known in X-ray technology and isotopediagnosis. They consist mostly of a vacuum tube containing a lightscreen behind the inlet surface which is followed in optical contact bythe actual photocathode layer. The electron ray image is thereuponproduced by a system of electrodes to which voltages of different valuesare applied, electron optically upon a semi-conducting plate, possiblyof smaller size.

As compared to known devices the device of the present invention has theadvantage that it can use semi-conducting plates with a small diameter.Furthermore, the proof probability of gamma radiation is considerablybetter due to the good absorption of electrons, than in the case ofdirect reception of gamma ray image in the semi-conducting layer.

The proof probability can be primarily increased by the use of ascintillation crystal, such as thallium activated sodium iodide, asprimary ray detector. This has can be produced in sufficiently largesizes as single crystals having the size of the bodily organ beingexamined. lnstead of a single crystal of corresponding size a matrix ofmany individual crystals can be used which are located one next to theother. The releasing capacity of this arrangement is limited, however,by the size of the screen of the crystal matrix. There is also thepossibility of using steamed upon layers of scintillating material.

The natural result of large layer thicknesses is that the light producedduring an absorption procedure in the scintillation crystal is widenedbefore it reaches the photo-cathode coupled to the crystal. Theresulting absorption of light division resulting from a single gammaquantum and thus the distribution of electrons released from thephoto-cathode, have a more or less great widening dependant upon thegeometry of the arrangement. The electornic optical representation ofthis practically gauss-shaped light and electron division upon thesemi-conducting plate results, therefore, in an image spot withcorresponding extension and intensity distribution of electronsstrikingthe semi-conducting plate.

The location of the maximum or the core point of this intensitydistribution corresponds to the location of the striking point of theinitial gamma quantum. In order to localize this striking point it istherefore necessary to determine the core point of the intensitydistribution. This can take place by determining the corresponding corepoints in the two directions provided by the stripshaped contacts.

To make possible the core determination with sufficient'precision thestrip-shaped screen formulation of the semi-conducting contacting unitmust be so narrow, or the size of the electronic optical image must beso selected, that the image spot of the. electronic distribution shouldcover at least a surface upon which there are nine (3 X 3) intersectionpoints of the electrodes. In case of semi-conducting plates used inelectronic optical vacuum changers from about 10 to strips aresufficient for the above purposes in order to produce an image sharpnessrequired for images now in use.

The semi-conducting plate can consist of known semi-conductors, such as,for example, silicon or germanium. Electrons striking the plate andabsorbed by it have through the electrostatic acceleration in anelectronic optical representation depending upon the accelerationvoltage an energy of 10 to 40 keV and they produce in the striken layerpairs of holes of electrons which are collected upon the strip-likeelectrodes. Consequently,charging impulses are produced upon theelectrode strips the size of which depends in addition to theacceleration voltage upon the number of the striking electrons. Thus animpulse height distribution will be registered upon the participatingelectrode strips which corresponds to the electron distribution in theimage spot. Then the core point of the x and y coordinates (the twostrip directions) can be easily determined in a known manner, forexample, by means of a digital calculator or by the use of analogouscircuits as they are used, for example, in a gamma camera according toAnger. The reproduction of the image is possible by known reproducingdevices, such as, for example, an XY-oscillograph, a telescopic screen,image printers, etc.

The sum of all impulse values appearing upon the electrode strip isproportional to the totally formed charge carrier, i.e., when theacceleration voltage is given, to the number of all striking electrons.The number of electrons is proportional to the energy of the absorbedgamma quantum, to the extent that it is absorbed by the photo effect. Byanalysing the impulse value of the total signal, for example, by meansof a one channel discriminator, it is possible to find certainoccurrences, for example, those released by a gamma quantum of aspecificenergy. This makes it possible to separate rays which are different inenergy, for example, to separate distributing stray rays or undergroundrays from the useful rays. In order to provide a summing signal it issufficient to use only signals upon the electrode strips upon one of thesurfaces of the semiconducting plate, since both sides of thesemiconducting plate participate in the collection of formed chargecarriers.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawingsshowing by way of example only, a preferred embodiment of the inventiveidea.

In the drawings: I

FIG. 1 is a sectiln through an electronic optical image magnifierwherein in accordance with the present invention the released electronbundle. is represented upon a semi-conducting plate as'an outlet screen.

FIG. 2 is a perspective view of a semi-conducting plate on an enlargedscale.

FIG. 3 is a diagram of the electronic circuit by means of which the corepoints of the striking surfaces of the electron bundle upon thesemi-conducting plate can be determined. A

FIG. 1 shows an image magnifier l with a glass case 2. The photo-cathodelayer 3 located within the case at its inlet side consists in theillustrated device of antimony activated by caesium. It is followed byannular electrodes 4, 5 and 6 extending concentrically to the cathode 3,as well as the anode 7. The anode is closed by a semi-conducting plate 8lying at the outlet window 9 of the image magnifier. In front of theinlet window 10 there is provided the light conducting device 12 havingsilicon oil used as the optical coupling layer 11 and provided at itsfree end with a further coupling layer 13 which also consists of siliconoil and which is connected to the scintillation crystal 14.

The silicon oil can be replaced by other coupling means, such as theknown optical luting.

In the illustrated example, organs marked with gamma ray conductors arepictured in the crystal 14 with the use of a parallel hole collimator14'. Gamma rays-passing through the holes of the collimator 14 which areindicated by arrows 15 in FIG. 1, are absorbed in the scintillationcrystal 14 while sending out light. They light thus produced istransmitted through the glass rods 12 serving as light conductors andhaving adiamet er of 7 mm, to the photo-cathode 3 and releases electronsthere. The electrodes 3 to 7 impress the electrons electronicallyoptically in a known manner upon the semi-conducting plate 8. The plateis provided upon both surfaces with strip contacts separated from eachother, as electrodes. The electrodes 16 directed to the cathodeconstitute in the semi-conductor of the described type surface locklayer counters and the outlet window 9, the direction of which ischanged by relatively to the strips 16, consist of steamed on aluminum.The semi-conducting plate in the illustrated example consists of n-typesilicon, has a thickness of 300 p. and a diameter of about 30 mm.; itdissolves the electron spot released by the rays 15 and produced byimage magnifying electron optics into individual strips which are shownsectionwise in FIG. 2 and which form electron hole pairs collected forlocalizing. The intersections of electrode strips 16 and 17 struck bythe electron spot operate then as surface lock layer detectors similarto counter diodes.

The determination of the striking location of the electron spot or ofits center. takes place in the gamma cameras in a manner known per se byanalog core formation. For clearer representation FIG. 3 shows only someof the electrode strips 16 and 17 which are actually present in thisembodiment; they are connected by high ohmic resistances 16' and 17 withthe coresponding dc. voltage source 34. As indicated in FIG. 3, in thestrips 18 and 22 (corresponding to 16) and in the transversely extendingelectrode strips 23 to 27 (corresponding to 17) are collected electronhole pairs produced by the electron bundle penetrating into the spot 45;they are amplified in the charge-sensitive preamplifiers 18' to 22' and23' to 27 to signals which can be further treated. The signals X, whichrefer to the istrips 18 to 22 and the amount of which corresponds to thepart of charge carriers from the electron spot 45 collected on one side,are measured in the coordinate circuit 28 corresponding to the locationof the corresponding electrode strip, i being the number of thecontinued counting of strips and x and the x-coordinate. For themeasurment the signal x,- is impressed by a factor a,- with the use of avoltage divider from the resistances 35 to 44. By a suitable selectionof resistances 35 to 44 the measuring factors a, constitute discretecoordinate values of the corresponding strips i in the xdirection. Forthis suitably selected resistances are used which produce voltagedividers, the ratio of which corresponds to a and is i/i There i is therunning number and i the largest available number of strips.Furthermore, the sums of thetwo resistances of each voltage divider areequal. v

The examined signals a, x, are summed up in a sum magnifier 29. Then asignal 2 a; x, is produced from which by division in the quotientforming device 31 through the sum signal of all unexamined signals x,

produced in the sum magnifier 30 the following standarized local signalis produced:

The X signal and Y signal produced in the corresponding manner by theuse of rear surface contact strips 2 5 to 27 in the coordinate circuit33 (identical to 28) are applied in this embodiment to the imagingelement 32 of an XY oscilloscope and are light tested with a Z signalwhich is produced by impulse'height discrimination of the unexamined sumsignal 2 x; in one channel discriminator 46. Then the core point of thespot 45 of the electron bundle striking the semi-conducting plate isrepresented in the XY" diagram of the element 32. Due to the formationof electrons indicated in FIG. 1 it corresponds to the place of theoriginal absorption location of a gamma quantum of the energy inthescintillation crystal 14 determined by the discriminator 46, so that thedesired visible representation is attained.

What is claimed is:

1. A device for representing organs marked by gamma rays, comprising incombination a semiconducting plate, electrode strips located on bothsides of the plate and extending parallel to each other, the directionof the strips on one side extending at an angle to the direction ofstrips on the other side, means connected with said plate for changingthe gamma quanta into electron bundles, a device connected with saidplate for producing signals corresponding to gamma ray images, saiddevice comprising calculating means for forming signals which correspondto core points of electron spots on said semi-conducting plate, and adevice for treating the last-mentioned signals and actuating visualizingmeans.

2. A device in accordance with claim 1, wherein the 5. A device inaccorance with claim 1, wherein the device for core formation includesan imaging element and an impulse discriminator located in the path ofthe representable signal directed to said imaging element. l l

1. A device for representing organs marked by gamma rays, comprising incombination a semi-conducting plate, electrode strips located on bothsides of the plate and extending parallel to each other, the directionof the strips on one side extending at an angle to the direction ofstrips on the other side, means connected with said plate for changingthe gamma quanta into electron bundles, a device connected with saidplate for producing signals corresponding to gamma ray images, saiddevice comprising calculating means for forming signals which correspondto core points of electron spots on said semi-conducting plate, and adevice for treating the last-mentioned signals and actuating visualizingmeans.
 2. A device in aCcordance with claim 1, wherein thesemi-conducting plate located in said image magnifier has a number ofelectrode strips adapted to the required localizing, whereby at leastthree pairs of strips are used for localizing an electron bundleproduced for the absorption of a gamma quantum.
 3. A device inaccordance with claim 2, wherein the number of electrodes carried by thesemi-conducting plate ranges from 10 to
 140. 4. A device in accordancewith claim 1, wherein the device for core formation includes a digitalcalculator.
 5. A device in accorance with claim 1, wherein the devicefor core formation includes an imaging element and an impulsediscriminator located in the path of the representable signal directedto said imaging element.